That's my PM:Gamma, not "Custom Gamma". Custom Gamma is the label of the per-image gamma on Image_Map nodes in the material room. Setting it to 1 is necessary for things that are grayscale data, not luminance/color data. For example, a displacement map records a pattern of displacement. It does not work the same if you treat that as a picture. It's not a picture. It's a matrix of displacement amounts. Changing those amounts leads to a different pattern than was intended.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)